Detection of damper motor mechanically disconnected from damper assembly

ABSTRACT

In an embodiment, a method of testing a HVAC unit for a disconnected damper motor is provided. An outside air section of a damper assembly is closed and air is circulated through the unit. If a discharge air temperature is not substantially equal to a return air temperature, the damper motor is determined to be disconnected. Otherwise, an economizing function having a free cooling target temperature is started. An outside air temperature is compared to the free cooling target temperature. If the outside air temperature is less than the free cooling target temperature, the damper motor is determined to be disconnected if the damper motor has been commanded to fully open the outside air section. If the outside air temperature is not less than the free cooling target temperature, the damper motor is determined to be disconnected if a discharge air temperature is not substantially equal to an outside air temperature.

CROSS REFERENCE TO RELATED INFORMATION

This application claims priority to U.S. patent application Ser. No.14/162,270, filed Jan. 23, 2014, titled Detection of Damper MotorMechanically Disconnected From Damper Assembly, now U.S. Pat. No.9,335,063 the contents of which are hereby incorporated herein in itsentirety.

TECHNICAL FIELD

This application relates to HVAC dampers and, more particularly, to HVACdamper motors.

BACKGROUND OF THE INVENTION

Damper assemblies are a common part of Heating, Ventilation, and AirConditioning (HVAC) units. A damper assembly may have two parts: anoutdoor air section which opens to receive outdoor air from outside thebuilding, and a return air section which opens to receive return airfrom inside the building. Opening one section of the damper assembly mayclose the other section and vice versa.

A HVAC unit controller adjusts a damper assembly to optimize energy use.For example, suppose a HVAC unit is cooling a building, and the outdoorair is cooler than the air inside the building. It is more efficient forthe HVAC unit to condition the outdoor air than to condition the returnair. Thus, the outdoor air section should be open at least partially. Anopportunity to save energy would be wasted if the outdoor air were keptout of the HVAC unit. Using outside air to cool the building in thismanner is known as “free cooling.”

Similarly, when cooling during hot outdoor weather or heating duringcold outdoor weather, it is more efficient for the HVAC unit tocondition the return air. The outdoor air section should be closed andthe return air section should be opened. Otherwise, the HVAC unit wouldwaste energy cooling or heating the outdoor air instead of the moresuitable return air.

A damper drive train opens and closes the sections of the damperassembly. A damper motor moves the damper drive train. The HVAC unitcontroller sends command signals to the damper motor to control themovement of the damper motor.

It is possible for the damper motor to become mechanically disconnectedfrom the damper assembly and damper drive train. When the damper motoris disconnected, the HVAC unit controller command signals cannot open orclose the sections of the damper assembly.

Energy savings can be missed if the outdoor air section is left closeddue to the disconnection. The HVAC unit may be missing the opportunityto utilize outdoor air which is more suitable for cooling than returnair. Likewise, energy can be wasted if the outdoor air section is leftopen due to the disconnection, because the HVAC unit may unnecessarilyheat or cool the less suitable outdoor air instead of the return air.

Conventionally, a disconnected damper motor is discovered, if ever, byan onsite technician visually inspecting the operation of the damperassembly. The HVAC unit may operate for a significant amount of timebefore a technician discovers the disconnection. It would be desirableif a HVAC unit could detect a disconnected damper motor automatically.The disconnected damper motor could be repaired more quickly, allowingthe HVAC unit to resume moving the damper assembly.

BRIEF SUMMARY OF THE INVENTION

In an embodiment, a method of testing a HVAC unit for a disconnecteddamper motor is provided. An outside air section of a damper assembly isclosed and air is circulated through the unit. If a discharge airtemperature is not substantially equal to a return air temperature, thedamper motor is determined to be disconnected. Otherwise, an economizingfunction having a free cooling target temperature is started. An outsideair temperature is compared to the free cooling target temperature. Ifthe outside air temperature is less than the free cooling targettemperature, the damper motor is determined to be disconnected if thedamper motor has been commanded to fully open the outside air section.If the outside air temperature is not less than the free cooling targettemperature, the damper motor is determined to be disconnected if adischarge air temperature is not substantially equal to an outside airtemperature.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1A depicts a HVAC unit with the outside air section of the damperassembly closed;

FIG. 1B depicts a HVAC unit with the outside air section and the returnair section of the damper assembly both partially open;

FIG. 2 depicts a test for determining if a damper motor is disconnectedin accordance with an exemplary embodiment of the present invention; and

FIG. 3 depicts an alternate test for determining if a damper motor isdisconnected in accordance with an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

In the following discussion, numerous specific details are set forth toprovide a thorough explanation. However, such specific details are notessential. In other instances, well-known elements have been illustratedin schematic or block diagram form. Additionally, for the most part,specific details within the understanding of persons of ordinary skillin the relevant art have been omitted.

Referring to FIGS. 1A and 1B, depicted is a Heating, Ventilation, andAir Conditioning (HVAC) unit 100 including controller 102. HVAC unit 100has damper assembly 104. Damper assembly 104 comprises outside airsection 106 and return air section 108. Outside air section 106 andreturn air section 108 may be composed of blades which can be opened andclosed to control airflow. Outside air section 106, when open, receivesair from outside the building. Return air section 108, when open,receives air returned from inside the building.

HVAC unit 100 has indoor blower 110. Indoor blower 110 pulls air fromthe building and pushes air into the building.

HVAC unit 100 also has a refrigerant system which can mechanically coolair flowing through the unit. This air in turn cools the building. HVACunit 100 may use mechanical cooling as an alternative to or in additionto free cooling.

HVAC unit 100 also contains sensors that can sense air temperaturesrelated to cooling the building. These sensors include temperaturesensors 112, 114, and 116. Outside air temperature (OAT) sensor 112measures the temperature of the outside air that outside air section 106would receive if open. Return air temperature (RAT) sensor 114 measuresthe temperature of the return air that return air section 108 wouldreceive if open. Discharge air temperature (DAT) sensor 116 measures thetemperature of air being discharged from HVAC unit 100 into thebuilding.

Generally speaking, a building thermostat or building energy managementsystem informs controller 102 on the cooling needs of the building, andcontroller 102 instructs HVAC unit 100 on how to respond to thosecooling needs. HVAC unit 100 may be referred to as a Roof-Top Unit(RTU). However, unit 100 is not necessarily located on a rooftop.

A damper drive train moves sections 106 and 108 in opposite directions.For example, when the blades of outside air section 106 are completelyclosed, return air section 108 is completely open, and vice versa. Whenoutdoor air section 106 is completely closed, no outdoor air may flowthrough outside air section 106, and the maximum amount of return airmay flow through return air section 108. When return air section 108 iscompletely closed, no return air may flow through return air section108, and the maximum amount of outdoor air may flow through outdoor airsection 106. Outside air section 106 is completely closed in FIG. 1A.

As one section gradually opens, the other section gradually closes. Whenboth sections are partially open, air flows through both sections ofdamper assembly 104. Outside air section 106 and return air section 108are both partially open in FIG. 1B.

HVAC unit 100 has a Free Cooling Target Temperature variable thatcontrols the operation of the damper assembly. If the discharge airtemperature is below the Free Cooling Target Temperature, HVAC unit 100closes outside air section 106 at least partially. If the discharge airtemperature is above the Free Cooling Target Temperature, HVAC unit 100opens outside air section 106 fully. In an embodiment, this free coolingtarget temperature is 55 degrees Fahrenheit.

The damper drive train is mechanically attached to a damper motor.Controller 102 commands the damper motor to move to a specifiedposition. The damper motor responds to the command with a feedbacksignal communicating the position of the damper motor as the drive trainopen or closes damper assembly 104. When the damper motor isdisconnected from the damper drive train, controller 102 command signalsto the damper motor do not move damper assembly 104. HVAC unit 100 mayoperate inefficiently as previously mentioned. However, the damper motormay still move and the feedback signal may still change to communicatethe position of the damper motor.

Using the damper motor, indoor blower 110, and sensors 112, 114, and116, controller 102 may perform an automatic test that determines if thedamper motor is disconnected. Computer-readable instructions forperforming the test may be provided to controller 102 as part of itsfirmware. By performing the test periodically, controller 102 mayautomatically discover a disconnected damper motor.

Referring to FIG. 2, depicted is a test 200 for determining if thedamper motor is disconnected. Test 200 may be performed when (1) theoutside air is determined to be acceptable for free cooling and (2) atemperature difference above a certain temperature preset value existsbetween the outside air temperature and the return air temperature. Thetemperature preset value is preferably between 5 and 10 degreesFahrenheit.

Test 200 is preferably performed at the initiation of the Pre-Cooloperation mode of HVAC unit 100. When the Pre-Cool mode is enabled by auser, controller 102 initiates the Pre-Cool mode in response to thefirst cooling demand of the building after night setback. Night setbackis the time when the building goes from unoccupied to occupied status.In the Pre-Cool mode, controller 102 conserves energy by using freecooling and not mechanical cooling.

At 202, controller 102 signals the damper motor to hold outside airsection 106 closed and return air section 108 open. At 204, controller102 signals indoor blower 110 to circulate air through HVAC unit 100. At206, controller 102 waits for a stabilization period, for example fiveminutes. The stabilization period is preferably long enough for air toflow across return air temperature sensor 114, through unit 100, andacross discharge air temperature sensor 116.

At 208, controller 102 compares the discharge air temperature fromdischarge air temperature sensor 116 with the return air temperaturefrom return air temperature sensor 114. If outside air section 106 isclosed, the discharge air temperature should be substantially equal tothe return air temperature. Otherwise, the damper motor is disconnected.

Due to factors such as temperature sensor accuracy and warming of theair as it flows past the motor of indoor blower 110, the return airtemperature and discharge air temperature may be close but not exactlyequal even when outside air section 106 is fully closed. The return airtemperature and discharge air temperature may be consideredsubstantially equal when the difference between them is below acomparison threshold. The comparison threshold may be the temperaturepreset value.

It is possible for the damper motor to still be disconnected when thedischarge air temperature and return air temperature are approximatelyequal. For example, the damper motor could have become disconnected whenoutside air section 106 was already closed. Thus, additional testing isnecessary.

At 210, controller 102 starts its economizing function. Controller 102adjusts damper assembly 104 to attempt to achieve the Free CoolingTarget Temperature as the discharge air temperature. In other words,controller 102 moves damper assembly 104 as necessary to raise and lowerthe discharge air temperature. Controller 102 attempts to keep thedischarge air temperature as close as possible to the Free CoolingTarget Temperature.

During the economizing function, HVAC unit 100 performs no mechanicalcooling. Because the outside air is suitable for free cooling, outsideair section 106 should be at least partially open during the economizingfunction.

At 212, controller 102 waits for a second stabilization period while theeconomizing function continues. As an example, this second stabilizationperiod could be five minutes. This second stabilization period ispreferably long enough for the damper motor to reach its target positionand stop moving, and then for air to flow across sensors 112 and/or 114(depending on the position of damper assembly 104), through unit 100,and across discharge air temperature sensor 116.

At 214, controller 102 determines if the outside air temperature is lessthan the free cooling target temperature. If the outside air temperatureis less than the free cooling target temperature, test 200 proceeds to216. If the outside air temperature is greater than or equal to the freecooling target temperature, test 200 proceeds to 218. 216 and 218 detecta damper motor which became disconnected when outside air section 106was closed or mostly closed. A damper motor which became disconnectedwhen outside air section 106 was open would have been detected at 208.

At 216, if the outside air temperature is less than the free coolingtarget temperature, the economizing function should have closed outsideair section 106 at least partially. However, if the damper motor isdisconnected with outside air section 106 closed or mostly closed, thedischarge air temperature will be substantially equal to the return airtemperature. This return air temperature is ordinarily higher than thefree cooling target temperature.

The economizing function will therefore attempt to reduce the dischargeair temperature, continually commanding the damper motor to open outsideair section 106 further. Eventually, at least after the secondstabilization period at 212, the economizing function will havecommanded the damper motor to fully open outside air section 106.Consequently, the feedback signal from the damper motor will indicateoutside air section 106 is fully open, though damper assembly 104 willnot have moved due to the disconnected damper motor.

Therefore, at 216, if outside air section 106 has been commanded to befully open according to the feedback signal from the damper motor, test200 determines the damper motor is disconnected from the damper drivetrain. Otherwise, test 200 does not determine the damper motor isdisconnected.

At 218, if the outside air temperature is greater than the free coolingtarget temperature, the economizing function should have fully openedoutside air section 106. Due to the fully open outside air section 106,the discharge air temperature from discharge air temperature sensorshould be substantially equal to the outside air temperature fromoutside air temperature sensor 112. If the discharge air temperature andthe outside air temperature are not substantially equal, test 200determines the damper motor is disconnected from the damper drive train.Otherwise, test 200 does not determine the damper motor is disconnected.Again, the two temperatures need not necessarily be exactly equal to besubstantially equal. Instead, their difference can be below a threshold,and the threshold can be the temperature preset value.

Both 214 and 218 use an outside air temperature reading from outside airtemperature sensor 112. Because the outside air temperature is unlikelyto change meaningfully between 214 and 218, the same outside airtemperature reading may be used at 214 and reused at 218. Alternately, anew outside air temperature reading may be obtained and used for 218.

Referring to FIG. 3, depicted is an alternate test 300 for determiningif the damper motor is disconnected. Test 300 may be performed in placeof test 200. Like test 200, test 300 may be performed when (1) theoutside air is determined to be acceptable for free cooling and (2) atemperature difference above a certain temperature preset value existsbetween the outside air temperature and the return air temperature.Again, the temperature preset value is preferably between 5 and 10degrees Fahrenheit. During test 300, all mechanical cooling and anyinstalled heating (gas or electric) by HVAC unit 100 is off.

At 302, controller 102 commands the damper motor to close outside airsection 106, then controller 102 waits for the damper motor feedbacksignal to indicate outside air section 106 is closed. At 304, controller102 turns on indoor blower 110. Indoor blower 110 circulates air throughthe unit as shown in FIG. 1A. At 306, controller 102 waits for astabilization period to pass. The stabilization period may be fiveminutes. The stabilization period is preferably long enough for air toflow across return air temperature sensor 114, through unit 100, andacross discharge air temperature sensor 116.

At 308, controller 102 compares the discharge air temperature fromdischarge air temperature 116 to the return air temperature from returnair temperature sensor 114. If the return air temperature and dischargeair temperature are not substantially equal, test 300 determines thedamper motor is disconnected. Otherwise, outdoor air section 106 isproperly closed.

At 310, while indoor blower 110 continues to circulate the air,controller 102 records the absolute value of the difference between thedischarge air temperature and the outside air temperature. At 312,controller 102 starts its economizing function. Because the outside airis suitable for free cooling, outside air section 106 should be at leastpartially open during the economizing function. At 314, controller 102waits for a second stabilization period, which again may be fiveminutes. This second stabilization period is preferably long enough forthe damper motor to reach its target position and stop moving, and thenfor air to flow across sensors 112 and/or 114 (depending on the positionof damper assembly 104), through unit 100, and across discharge airtemperature sensor 116.

At 316, controller 102 determines the absolute value of the differencebetween the discharge air temperature and the outside air temperature.If the damper motor is not disconnected, the damper motor opened outsideair section 106. The absolute value recorded at 310 should therefore begreater than the absolute value determined at 316. If the absolute valuerecorded at 310 is less than or equal to the absolute value determinedat 316, test 300 determines the damper motor is disconnected. Otherwise,test 300 does not determine the damper motor is disconnected.

Both 310 and 316 use an outside air temperature reading from outside airtemperature sensor 112. Because the outside air temperature is unlikelyto change meaningfully between 310 and 316, the same outside airtemperature reading may be used at 310 and reused at 316. Alternately, anew outside air temperature reading may be obtained and used for 316.

If test 200 or test 300 determines the damper motor is disconnected,unit 100 may generate an alarm code. The alarm code may be an indicationthe damper motor is disconnected. The alarm code may be displayed on ascreen of controller 102. If controller 102 is connected to a centralenergy or building management system, the alarm code may also betransmitted from controller 102 to that system. The purpose of the alarmcode is to notify a person that the damper motor must be reconnected.

It is noted that the embodiments disclosed are illustrative rather thanlimiting in nature and that a wide range of variations, modifications,changes, and substitutions are contemplated in the foregoing disclosureand, in some instances, some features of the present invention may beemployed without a corresponding use of the other features. Many suchvariations and modifications may be considered desirable by thoseskilled in the art based upon a review of the foregoing description ofvarious embodiments.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A method of testing a HVAC unit for adisconnected damper motor, the method comprising: closing an outside airsection of a damper assembly of a HVAC unit; circulating air through theHVAC unit; comparing a discharge air temperature to a return airtemperature; if the discharge air temperature is not substantially equalto the return air temperature, determining a damper motor isdisconnected from the damper assembly; and if the discharge airtemperature is substantially equal to the return air temperature:recording a first absolute value, the first absolute value comprising adifference between a first comparison discharge air temperature and afirst comparison outside air temperature; starting an economizingfunction of a controller of the HVAC unit, the economizing functioncomprising a free cooling target temperature; comparing the firstabsolute value to a second absolute value, the second absolute valuecomprising a difference between a second comparison discharge airtemperature and a second comparison outside air temperature; and if thefirst absolute value is not greater than the second absolute value,determining the damper motor is disconnected from the damper assembly.2. The method of claim 1, wherein the economizing function comprisesadjusting the damper assembly to make the temperature of air dischargedfrom the HVAC unit equal to the free cooling target temperature.
 3. Themethod of claim 1, wherein the first comparison outside air temperatureis reused as the second comparison outside air temperature.
 4. Themethod of claim 1, wherein the first comparison outside air temperatureis not reused as the second comparison outside air temperature.
 5. Themethod of claim 1, further comprising, in response to determining thedamper motor is disconnected from the damper assembly, generating anindication the damper motor is disconnected.
 6. The method of claim 1,further comprising, after circulating air through the HVAC unit, waitingfor a stabilization period.
 7. The method of claim 1, furthercomprising, after starting the economizing function, waiting for astabilization period.
 8. A HVAC unit controller for testing a HVAC unitfor a disconnected damper motor, the unit controller configured to:close an outside air section of a damper assembly of a HVAC unit;circulate air through the HVAC unit; compare a discharge air temperatureto a return air temperature; if the discharge air temperature is notsubstantially equal to the return air temperature, determine a dampermotor is disconnected from the damper assembly; and if the discharge airtemperature is substantially equal to the return air temperature: recorda first absolute value, the first absolute value comprising a differencebetween a first comparison discharge air temperature and a firstcomparison outside air temperature; start an economizing function of thecontroller, the economizing function comprising a free cooling targettemperature; compare the first absolute value to a second absolutevalue, the second absolute value comprising a difference between asecond comparison discharge air temperature and a second comparisonoutside air temperature; and if the first absolute value is not greaterthan the second absolute value, determine the damper motor isdisconnected from the damper assembly.
 9. The HVAC unit controller ofclaim 8, wherein the economizing function comprises adjusting the damperassembly to make the temperature of air discharged from the HVAC unitequal to the free cooling target temperature.
 10. The HVAC unitcontroller of claim 8, further configured to reuse the first comparisonoutside air temperature as the second comparison outside airtemperature.
 11. The HVAC unit controller of claim 8, further configuredto not reuse the first comparison outside air temperature as the secondcomparison outside air temperature.
 12. The HVAC unit controller ofclaim 8, further configured to, in response to determining the dampermotor is disconnected from the damper assembly, generate an indicationthe damper motor is disconnected.
 13. The HVAC unit controller of claim8, further configured to, after circulating air through the HVAC unit,wait for a stabilization period.
 14. The HVAC unit controller of claim8, further configured to, after starting the economizing function, waitfor a stabilization period.